Stress-rupture perforated strip and method of production



April 25, 1967 F. A. wrr'r 3,315,335

STRESS-RUPTURE PERFORATED STRIP AND METHOD OF PRODUCTION Filed Jan. 17. 1964 L fi L I i PIE =2 lg If I Plus--3 l/VVE/VTGR FRANK A. W/TT .4 H0 me y United States Patent O 3,315,335 STRESS-RUPTURE PERFORATED STRIP AND METHOD OF PRODUCTION Frank A. Witt, Monroeville Borough, Pa., assignor to United States Steel Corporation, a corporation of Delaware Filed Jan. 17, 1964, Ser. No. 338,434 3 Claims. (Cl'. 29163.5)

This invention relates to the multiple perforation of relatively hard foil-like strip, sheet, and the like by subjecting same to pack rolling with relatively thicker strips of softer material, whereby the soft material is elongated and distends with it the hard material, resulting in its perforation by rupture.

The invention is applicable to the perforation of tinplate, steel, copper, bronze, nickel, silver, lead, and any other metallic, quasi-metallic, or other materials with similar physical properties as regards rupture on distension when rolled between more plastically extensible media.

The perforated strip of the invention is suitable as a filter medium, for example, as a substitute for woven mesh and steel wool in gas and liquid filters.

The invention is further described in conjunction with the accompanying drawings wherein:

FIGURE 1 diagrammatically depicts a sandwich pack construction of hard and soft materials in process of being reduced by rolling to produce the product of the invention.

FIGURES 2 and 3 depict optional variations of pack construction suitable for rolling to obtain the product of the invention.

FIGURE 4 is a pen and ink tracing of a photograph of an example of the product of the invention, at 20X magnification.

In more detailed description of the invention, FIGURE 1 shows relatively hard sheet material 1, of relatively low ductility, in a sandwich pack with softer and more ductile material which is susceptible of relatively ready reduction by rolling. The figure depicts the material before and after rolling, from left to right, between work rolls 3, having back-up rolls 4, in a conventional cold reduction mill for steel strip and the like.

In the rolling operation, the total thickness of the pack is reduced; however, the thickness of the strip having low ductility undergoes a relatively low proportionate reduction in actual thickness. Principal reduction in the pack is due to the soft elements thereof, which elongate and carry along the low ductility material, which latter material appears to become partially imbedded in the soft material during rolling. The resulting stress of the low ductility material results in its extension by multiple rupture, as shown in FIGURE 4, wherein the base material is 5 and the perforations are 6.

As shown in FIGURE 2, several low ductility strips 1a, 1b, may be rolled simultaneously. Also, as shown in FIGURE 3, the soft material, for stressing the material of low ductility, need be on no more than one side of the latter.

To further describe the invention, reference is made to specific materials and procedures which produced the products shown in FIGURE 4.

3,315,335 Patented Apr.-25, 1967 Steel of the following composition was employed for both the carrier and the perforated base material.

with the balance iron and residual amounts of other elements.

Stock of the above composition, subsequently tinned and rolled full-hard, was employed as core 1 of FIGURE 1. This material was 0.0008 inch thick and had a tensile yield strength of 115,000 p.s.i.

The outer layers 2 of a pack such as shown in FIGURE 1 were of annealed blackplate, of the foregoing composi tion, 0.0066 inch thick and having a tensile yield strength of approximately 45,000 p.s.i.

The product of FIGURE 4 was produced by rolling the pack to an overall reduction of 60%. Reductions of 40% yielded comparative ruptures.

Thiclmesses of 0.010 inch in the outer material 2 yielded similar results. With this thickness incipient perforation was noticeable at about 30% pack reduction. Increasing the reduction increased the amount of perforation. The thickness of the perforated strip product was in most cases about 0.0005 to 0.0006 inch, when commencing with the 0.0008 inch material.

While the foregoing examples describe results with tinplate perforation, it will be appreciated by those skilled in the art that other materials may be perforated.

Also, other concomitant pack materials may be employed, so long as they are sufiiciently adapted to flow more readily under rolling than the material being perforated and are of sufficient thickness, together with strength characteristics, to carry the material being perforated with them upon pack reduction.

For the softer material to carry the harder material with it, the initial thickness of the former should be several times that of the latter, and may be in the order of five to ten times. Excessive thicknesses of the softer material are generally undesirable from an economic standpoint.

As is apparent from FIGURE 4, the perforations are relatively uniform in size and fairly evenly spaced as would be the case at any given pack reduction. The perforations present an irregular outline, resulting from the tearing action imposed.

While several specific embodiments of the invention have been shown, it will be understood that these embodiments are for the purpose of illustration and description, and that various other forms may be devised within the scope of the invention, as defined in the ap pended claims.

I claim:

1. The process of stress-rupture perforating of relatively non-reducible, hard, low ductility, foil-like strip material comprising the steps of laying said relatively lowductility strip between two thicker relatively ductile strips,

rolling the composite in a pack, thereby elongating t-he ductile strips which carry with them the said relatively non-ductile strip and thus extending and multiply rupturing said non-ductile strip to produce relatively uniform and evenly spaced perforations therein, and thereafter separating the three strips.

2. The process of claim '1 in which said relatively nonductile strip is hard rolled steel, while the said ductile strips are annealed steel.

3. The process of claim 1 in which said relatively nonductile strip is of about 0.0008 inch thickness, with a tensile yield strength of approximately 115,000 p.s.i., while said ductile strips are annealed steel having a tensile yield strength of about 45,000 p.s.i.

References Cited by the Examiner UNITED STATES PATENTS CHARLES W. LANHA'M, Primary Examiner.

H. D. HOINKES, Assistant Examiner. 

1. THE PROCESS OF STRESS-RUPTURE PERFORATING OF RELATIVELY NON-REDUCIBLE, HARD, LOW DUCTILITY, FOIL-LIKE STRIP MATERIAL COMPRISING THE STEPS OF LAYING SAID RELATIVELY LOWDUCTILITY STRIP BETWEEN TWO THICKER RELATIVELY DUCTILE STRIPS, ROLLING THE COMPOSITE IN A PACK, THEREBY ELONGATING THE DUCTILE STRIPS WHICH CARRY WITH THEM THE SAID RELATIVELY NON-DUCTILE STRIP AND THUS EXTENDING AND MULTIPLY RUPTURING SAID NON-DUCTILE STRIP TO PRODUCE RELATIVELY UNIFORM AND EVENLY SPACED PERFORATIONS THEREIN, AND THEREAFTER SEPARATING THE THREE STRIPS. 